1. Field of the Invention
This disclosure relates to media handling within a printing apparatus, and more particularly, to a calibration and diagnostic system for use within the paper path of a printing apparatus to determine media speed characteristics, position in the paper path and skew.
2. Description of Related Art
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the information areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Generally, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet. Such an electrophotographic printing process is shown in U.S. Pat. No. 6,137,989, which is incorporated herein by reference.
In high-speed media or paper handling applications, it is very difficult to diagnose the root cause of any problems because it is essentially impossible to see what is going on inside the machine. This is both because the physical space within the machine is so tight that what one can see is limited, plus the fact that the paper is moving so quickly. Typically, all diagnostics are performed by looking at sheet arrival and departure times at various discrete sensors. No information about paper skew is generally available. Other defects, such as, smear or paper damage must be solved indirectly.
U.S. Pat. No. 5,313,253 issued May 17, 1994 to Michael J. Martin et al. is concerned with paper path signature analysis and discloses an apparatus which utilizes output from various idler rolls throughout the machine paper path to detect abnormalities. The constantly monitored and instantaneous velocity reading are compared with a base line velocity signature established at the factory. If the constantly monitored velocity profile is not within the pre-established operation parameters as set at the factory, automatic machine adjustment procedures are initiated and/ort automatic service alerts are issued.
A method of changing the reference timing of a sheet transport control in an imaging forming device for determining the validity of the timing of a sheet by comparing the actual timing of a sheet with a given reference timing is shown in U.S. Pat. No. 5,528,347 issued Jun. 18, 1996. Actual timings for a plurality of copy sheets in relation to a predetermined sensor are stored in memory. A typical time period from a plurality of copy sheets is then determined in relation to the sensor and the reference timing for the sensor is adjusted based upon the typical time period for the sensor.
U.S. Pat. No. 5,859,440 issued Jan. 12, 1999 to Thomas Acquaviva discloses a dual mode non-contact optical sheet edge detection system for detecting either fully transparent or regular sheet being fed in a sheet transport of a reproduction system. The system utilizes an illumination source for illuminating the potential sheet edge area at an angle to generate a detectable sheet edge shadow from transparent sheets, and an optical detection system remotely detecting the generated edge shadow to provide sheet edge location or timing information to a control system. Preferably, the sheet edge is held spaced above the illuminated sensor and illuminated target area to enhance the shadow effect.
An apparatus and method for correcting top edge sheet misregistration using a sensor array is disclosed in U.S. Pat. No. 6,137,989 issued Oct. 24, 2000 to Lisbeth S. Quesnel. An array sensor is placed in the paper path prior to transfer. A signal is generated indicating the position of the sheet. As a function of the signal, the print controller causes the image to be exposed and developed on the photoreceptor in alignment with the sheet position. The aligned image is then transferred to the sheet.
U.S. Pat. Nos. 6,168,153 B1 and 6,173,952 B1 issued Jan. 2, 2001 and Jan. 16, 2001, respectively, to Paul N. Richards et al. disclose a sheet handling system for correcting the skew and/or transverse position of sequential sheets, especially those moving in a process direction in a sheet transport of a reproduction apparatus. The system employs sensor arrays in deskewing and/or side registering sheets.
Some of these technologies are quite sophisticated, utilizing various embedded sensors, digitally controllable stepper motors and high speed computational capability, all of which add up to a significant level of equipment cost, which, while justified in a high-end printer, might be considered exorbitant in a smaller, less expensive device.
Furthermore, while these systems provide control over certain aspects of machine behavior that are designed to be controlled, there will always be unintended sources of variation due to various types of defects and malfunctions which these systems can neither compensate for, nor diagnose.
Even though the above-mentioned prior art is useful, there is still a need, in printers for improvements in paper path diagnostic systems.
Accordingly, a paper path and diagnostic system is disclosed that answers the above-mentioned problem by using precisely aligned slots strategically placed in the frame of a printer along its paper path and positioning scanner bars within those slots to “watch” the paper as it goes by. The scanner bars will monitor the paper as it is fed, looking for any irregularities, such as, skew at each station. If, for example, skew is detected, detailed information is included in the scanner data to help identify the associated vectors and root cause of the skew. If ladder chart paper is used, the velocity of the sheet and the motion quality information can also be extracted.
While the disclosure will be described hereinafter in connection with a preferred embodiment thereof, it will be understood that limiting the disclosure to that embodiment is not intended. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.